1. Field of the Invention
Described herein are devices relating to lighting fixtures, such as suspended linear lighting fixtures, that are well suited for use with solid state lighting sources, such as light emitting diodes (LEDs).
2. Description of the Related Art
Lighting fixtures, such as Troffer-style lighting fixtures, are ubiquitous in commercial office and industrial spaces throughout the world, oftentimes being designed to have a spatially convenient and aesthetically pleasing linear appearance. To this end, many of these lighting fixtures house linear elongated fluorescent light bulbs that span the length of the troffer. These lighting fixtures can be mounted to or suspended from ceilings, and can be at least partially recessed into the ceiling, with the back side of the troffer protruding into the plenum area above the ceiling. U.S. Pat. No. 5,823,663 to Bell, et al. and U.S. Pat. No. 6,210,025 to Schmidt, et al. are examples of typical troffer-style fixtures.
More recently, with the advent of the efficient solid state lighting sources, troffers and other commercial lighting fixtures have been developed that utilize LEDs as their light source. LEDs are solid state devices that convert electric energy to light and generally comprise one or more active regions of semiconductor material interposed between oppositely doped semiconductor layers. When a bias is applied across the doped layers, holes and electrons are injected into the active region where they recombine to generate light. Light is produced in the active region and emitted from surfaces of the LED.
LEDs have certain characteristics that make them desirable for many lighting applications, such as troffers, that were previously the realm of incandescent or fluorescent lights. Incandescent lights are very energy-inefficient light sources with approximately ninety percent of the electricity they consume being released as heat rather than light. Fluorescent light bulbs are more energy efficient than incandescent light bulbs by a factor of about 10, but are still relatively inefficient. LEDs by contrast, can emit the same luminous flux as incandescent and fluorescent lights using a fraction of the energy.
In addition, LEDs can have a significantly longer operational lifetime. Incandescent light bulbs have relatively short lifetimes, with some having a lifetime in the range of about 750-1000 hours. Fluorescent bulbs can also have lifetimes longer than incandescent bulbs such as in the range of approximately 10,000-20,000 hours, but provide less desirable color reproduction. In comparison, LEDs can have lifetimes between 50,000 and 70,000 hours. The increased efficiency and extended lifetime of LEDs is attractive to many lighting suppliers and has resulted in their LED lights being used in place of conventional lighting in many different applications. It is predicted that further improvements will result in their general acceptance in more and more lighting applications, including commercial lighting fixtures. An increase in the adoption of LEDs in place of incandescent or fluorescent lighting would result in increased lighting efficiency and significant energy saving.
LEDs can be arranged in different ways in the above mentioned lighting fixtures, with some fixtures having LEDs incorporated into a linear lighting device and having a structure similar to a florescent tube. Many of these fixtures are suspended some distance from the ceiling, for example, by utilizing mechanical supports at either end of the fixture. This suspension arrangement allows the light to be positioned such that it illuminates more of a given room and is particularly useful in areas with higher ceilings.
One undesirable side effect of utilizing a suspended lighting fixture, due to the fixture's shadow and the lack of upward directed light (“uplight”), the ceiling and area directly above the suspended fixture does not receive sufficient lighting. This results in a dark area that obscures the view of ceiling and other structures above the suspended fixture, producing an obscuring “cave effect.” This cave effect distorts the perceived relationship in space between the walls and various objects in the room, resulting in an observer not being able to determine the spatial perimeters of the room, for example, the distance from the floor to the ceiling. This distortion effect on the senses can be especially true in large rooms with high ceilings and results in a sensation that is disorienting and unpleasant.